1. Field of the Invention
This invention relates generally to photonic switching arrays, and, more particularly, to a switching array based on microelectromechanical motion of overlapping polymer waveguides.
2. Description of the Related Art
One conventional photonic switch uses the Mach-Zehnder device architecture with non-linear optical crystals. Although eight-by-eight arrays have been fabricated, this type of switch is expensive to manufacture and difficult to fit on standard electro-optic packages. Commercially available non-linear optical crystal switches that fit on a single substrate are limited to two-by-two arrays. A larger array is yield-limited by its size, which is determined by the electro-optic coefficient of the non-linear crystal, usually LiNbO.sub.3, and by the applied voltage, which must comply with the material dielectric strength.
Another method of photonic switching is to convert the optical signal to an electrical signal, reconfigure the input-to-output channel assignment electronically, and convert the electrical signal back to an optical signal. This complicated procedure adds significant overhead to the signal propagation introduced by the decoder and modulator circuitry, thus increasing the time delay and the power consumption. This method is also limited by the bandwidth restrictions of the opto-electronic electronic converter which downgrade the optical network capabilities.
Electromechanical deflection of reflective surfaces has been used for waveguide photonic switching by means of microcantilevers or microbridges, as described in R. Watts et al., "Electromechanical Optical Switching and Modulation in Micromachined Silicon-on-Insulator Waveguides," 1991 IEEE International SOI (silicon-on-insulator) Conference Proceedings, pp. 62-63. A voltage supplies electrostatic attraction resulting in a deflection of the microcantilever or microbridge. When this technique is used in free space, alignment and vibration problems can occur.
Micromachining has recently been used for fabrication of diffraction gratings for spectral analysis and optical modulator switches because of the high resolution sculpting capability of this technique, as described in O. Solgaard et al., "Deformable grating optical modulator," Optics Letters, vol. 17, no. 9, 688-90 (May 1, 1992). Other approaches include a monolithic four-by-four photonic crossbar switch that has been fabricated for avionic systems using rib waveguides with etched facets and turning mirrors, and a multimode two-by-two optical switch in which micromachined pivoting silicon moving mirrors selectively direct optical beams from input fibers to output fibers. Vibration and alignment difficulties reduce the effectiveness of these techniques.
Polymeric waveguide technology has been used with ferroelectric liquid crystals to develop a six-by-six matrix switching array and provide guided wave connectivity to a multi-element spatial light modulator. The maximum operating temperature of this type of switch is about 60.degree. C., however, which is too low for aerospace, military, and automotive applications.
Aforementioned Ghezzo et al., Ser. No. 08/144,165, now pending discloses a switch which uses microelectromechanical motion of overlapping polymer waveguides. The principle of operation is based on modulation of optical energy transfer between overlapping polyimide waveguides which determines whether the incoming light remains in the initial waveguide or is partially transferred to the adjacent waveguide. This transfer depends on the mutual separation between waveguides, which is controlled by electrostatic or piezoelectric actuation.